Assassins in the Garden

This morning while deadheading the daylilies, I discovered a green assassin bug nymph on one of the buds. This was a welcome find since these insects are beneficial predators. Both the nymphs and adults are generalized feeders and will consume a number of different kinds of insects from small aphids to stinkbugs to large caterpillars. Unfortunately, like praying mantids, they also eat beneficial insects and even other assassin bugs as well.

Assassin bugs are members of the family Reduviidae in the order Hemiptera, and there are at least 160 known species in North America. These range in size from about .5 to 1.5 inches, and they vary in color from green to brownish to brightly colored. Their body shape varies from long and narrow like the green assassin bug, Zelus luridus, to much chunkier like some of the ambush bugs. One of the largest is the prehistoric-looking wheelbug, Aristus cristatus, which is characterized by a semicircular serrated crest on the dorsal side of its thorax. All species have long antennae, long legs, overlapping membranous wings that may be narrower than the abdomen, and a narrow head tapering to a distinct neck-like region. Their eyes are rather large and round and colored red in some.

In certain species, it is the adults who overwinter in protected spots. Females lay clusters of eggs on vegetation in warm weather, and these hatch into nymphs which are wingless and smaller and often differently colored than the adults. These molt at least 4 times before reaching maturity.

Like all the Hemiptera, the assassin bugs have a sharp needle-like feeding structure that they use to pierce the body of their prey and suck out digested body fluids. This beak or “rostrum” is short and 3 segmented in the assassin bugs and usually held underneath their body when not in use. Their forelegs are adapted for grabbing prey and may be sticky to help hold the victim in place while they inject their paralyzing venom and enzymes. Though the adults have wings, they are not good fliers. However, they can move very quickly when disturbed or when grabbing prey. Some of them stalk their prey; others lie in ambush among the vegetation. An internet search resulted in some rather gruesome video sequences of these insects capturing and feeding upon their hapless and still living prey! Watch out if you handle them since they are known to bite humans as well, and this can result in a painful burning sensation and occasionally an allergic response! There are species of assassin bugs, known as “kissing bugs” or bloodsucking conenoses, which suck blood from mammal hosts including humans. Although found throughout North America, they are more prevalent in the south and west where control measures may have to be taken to keep them out of houses.

Despite their status as fearsome predators, assassin bugs themselves are preyed upon by spiders, praying mantids, birds, and rodents. Given the prevalence of those in my garden, I wish my little nymph well on its journey through life, and I hope it stays well fed and camouflaged from the sharp eyes of the little wrens who patrol my garden daily!

The Ubiquitous Wood Sorrels

The growing conditions in our area this spring and early summer have been just wonderful for various weed species which have been, well, “growing like weeds” as the old cliché goes! One of the more vigorous groups has been the wood sorrels of the genus Oxalis. Although these plants prefer nutrient-rich moist soil, they tolerate many conditions from moist to dry and sun to shade and so can be found everywhere in your yard!

Yellow wood sorrel, Oxalis stricta, known also as sheep sorrel, toad sorrel, or sourgrass, is a very common native weed which is probably well known to most gardeners. This upright plant will grow among your flowers, shrubs or vegetables as well as in nursery- or greenhouse-grown container plants and lawns . It has clover-like alternate compound leaves with 3 heart-shaped leaflets. Its dainty flowers are yellow with 5 petals, and it blooms from mid-spring throughout the summer. The fruit is a pointed capsule which contains compartments to hold the seeds. When the capsules dry, they split open explosively and shoot seeds to distances of 10 feet or more. Seed production is this plant’s major method of reproduction and dispersal. The seeds themselves are rough and a bit sticky and can easily travel on shoes, clothing and equipment. Yellow wood sorrel is fairly easy to hand weed, and mulching can help prevent seeds from germinating. Many herbicides are not very effective on this plant except for possibly pre-emergent ones.

Creeping wood sorrel, Oxalis corniculata, looks very similar to yellow wood sorrel, but it is prostrate and often has reddish or purplish stems and comes in both green- or purple-leaved varieties. This species was introduced to North America long ago, most likely from Europe. Unlike O. stricta, it can spread by rooting from its stems, and broken stems or roots can regenerate, thus making it more difficult to control than yellow wood sorrel. You must try to pull out the entire plant. This is much easier to accomplish with young plants than with those that have already spread! It also tends to grow in cracks and crevasses as well as in and among groundcover plants such as sedums thus increasing the frustration of trying to get it out of the garden! Like its relative, it also reproduces by launching thousands of seeds from its capsules. Mulching can help control these to some extent. In turf, it is too low to be affected by mowing. Creeping wood sorrel is an alternate host of some disease-causing nematodes and curly top beet virus.

On the positive side, both of these weeds are edible. However, they both contain oxalic acid which, in high amounts, can be toxic enough to cause kidney failure. This can sometimes be a problem for livestock and for people if they consume too much. These plants should not be eaten by anyone with kidney disorders or rheumatoid arthritis. Purportedly, both have a sour, lemony flavor. The wood sorrels have been used in folk medicine as well. Ecologically, both species do provide nectar and pollen for some bees, flies and butterflies, and their seeds and foliage are eaten by mice, rabbits and deer.

Master Gardeners are volunteers trained by Penn State Extension Horticulture Educators. Once they complete their training, they cooperate with service agencies and community groups on a wide range of gardening projects. Their talents and energies are directed toward providing a link between their community and Penn State Cooperative Extension and Outreach.